The present invention is related to the acylation of thiazolidines using acyl halides in the presence of certain bases.
Substituted thiazolidines of the formula ##STR1## wherein R is haloalkyl, and each of R.sup.1 and R.sup.2 is hydrogen lower alkyl, are useful as antidotes against crop injury when used with various herbicides. Such compounds are disclosed, for example, in U.S. Pat. No. 4,319,031. Desirous plants such as crop plants can be protected against injury by thiocarbamate-type herbicides, alone or mixed with other herbicides, by adding to the soil a non-phytotoxic antidotally effective amount of a compound of the above formula.
Prior to the present invention, the primary methods for synthesizing these substituted thiazolidines have been by reacting a compound of the above formula (where C(O)--R is replaced by a hydrogen atom) with either
(a) an acid halide X--C(O)--R (where X is a halogen) in the presence of NaOH or other caustic (the Schotten-Baumann reaction), or
(b) an acid halide X--C(O)--R (where X is a halogen) in the presence of a base such as triethylamine.
Unfortunately, each of these reaction schemes suffers from low yields. In reaction (a) the yield is about 65% or less. In reaction (b) the yield is below 50%.
Additionally, a method for synthesizing other dichloroacetamides by treatment with chloral and sodium cyanide in aqueous sodium carbonate is known (British Patent No. 692,165 (1953); Chem. Abstracts (1954) 48: 8260 g). However, when this method is attempted to produce the above thiazolidines, only a small amount of the desired dichloroacetyl thiazolidine is made, with the major product being diacetyldisulfide.